1. Field of the Invention
The present invention relates to a voltage regulator for controlling output voltage of an alternator for use in an automotive vehicle. The output voltage is controlled by controlling excitation current supplied to a field coil of the alternator.
2. Description of Related Art
A voltage regulator that includes a detector for detecting disconnection in a circuit charging an on-board battery with output voltage of an alternator is disclosed in, for example, JP-A-56-150935 and JP-B2-2954374. The disconnection includes a situation where a charging wire is disconnected from a terminal and a situation where the charging wire itself is cut off. This definition will be applied to all the description in this specification.
In this voltage regulator, both an output voltage of the alternator and a terminal voltage of the on-board battery are detected. The disconnection in the charging circuit is detected based on a difference between the output voltage and the terminal voltage. Upon detection of the disconnection, a warning light is lit to inform a driver of the malfunction.
Since both of the output voltage of the alternator and the terminal voltage of the battery have to be detected in the conventional regulator described above, the number of terminals used for the detection increases. Accordingly, the voltage regulator becomes not only complex but also expensive.